This invention relates to the stabilization of microbicides. In particular, this invention relates to the improved stabilization of 3-isothiazolone microbicides.
Microbicides are used commercially to prevent the growth of microbes in a variety of loci, such as cooling towers, metal working fluid systems, paint and cosmetics. One of the more important classes of microbicides is 3-isothiazolones. Many 3-isothiazolones have achieved commercial success because they are very effective in preventing microbial growth under a wide variety of conditions and in a variety of loci. Among the most important 3-isothiazolones are 5-chloro-2-methyl-3-isothiazolone, 2-methyl-3-isothiazolone, 2-n-octyl-3-isothiazolone, 4,5-dichloro-2-n-octyl-3-isothiazolone and mixtures thereof.
Typical 3-isothiazolone products of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain between 0.5 and 35 percent by weight of the 3-isothiazolone mixture and a similar amount of a stabilizer. Concentrate compositions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone generally contain about 5 to 35 percent by weight of the 3-isothiazolone compounds and require about 10 to 25 percent by weight of a stabilizer. Dilute solutions of a 3:1 mixture of 5-chloro-2-methyl-3-isothiazolone and 2-methyl-3-isothiazolone contain about 0.5 to 5 percent by weight of the 3-isothiazolone compounds. These dilute solutions typically contain from 1 to 25 percent by weight of a stabilizer for the 3-isothiazolones.
While 3-isothiazolones are very effective microbicides, they suffer from being unstable under certain conditions. Without the presence of a stabilizer, many 3-isothiazolones chemically degrade and lose microbicidal efficacy, especially in aqueous systems. Much research has been devoted to stabilizing 3-isothiazolones.
Many of the methods developed to stabilize 3-isothiazolone compounds use inorganic salts. For example, the most commercially successful stabilizers for 3-isothiazolone compounds are metal nitrate salts. To be effective in stabilizing 3-isothiazolone compounds, high levels (for example 14% wt) of metal nitrate salts are typically required. The presence of these high salt levels can cause coagulation of latexes.
Some organic stabilizers have been developed for 3-isothiazolone compounds. For example, EP 411 750 A (Mattox) discloses the use of various organic compounds as stabilizers for 3-isothiazolones. Such organic compounds include dialkyl- and dicycloalkyl-carbodiimides. The problem with these organic compounds is that they work only in non-aqueous systems.
There is thus a continuing need for stabilizers for 3-isothiazolones that can be used in both aqueous and non-aqueous systems and do not cause coagulation of latexes.